Utils: Introduce a central porting.h for "simple porting stuff"

I figured it might be easier to keep track of active hack here and
also recognized includes that only exist for that reasons in user code
if it's always the same.

Change-Id: I4bf6af493443148cf30a6903d541cd9dc58946da
Reviewed-by: David Schulz <david.schulz@qt.io>

src/libs/utils/stringutils.h

@@ -27,6 +27,8 @@
 
 #include "utils_global.h"
 
+#include "porting.h"
+
 #include <QList>
 #include <QString>
 
@@ -36,12 +38,6 @@ QT_END_NAMESPACE
 
 namespace Utils {
 
-#if (QT_VERSION < QT_VERSION_CHECK(5, 14, 0))
-constexpr QString::SplitBehavior SkipEmptyParts = QString::SkipEmptyParts;
-#else
-constexpr Qt::SplitBehaviorFlags SkipEmptyParts = Qt::SkipEmptyParts;
-#endif
-
 // Create a usable settings key from a category,
 // for example Editor|C++ -> Editor_C__
 QTCREATOR_UTILS_EXPORT QString settingsKey(const QString &category);